Dram cells with vertical transistors

ABSTRACT

The invention includes a semiconductor structure having U-shaped transistors formed by etching a semiconductor substrate. In an embodiment, the source/drain regions of the transistors are provided at the tops of pairs of pillars defined by crossing trenches in the substrate. One pillar is connected to the other pillar in the pair by a ridge that extends above the surrounding trenches. The ridge and lower portions of the pillars define U-shaped channels on opposite sides of the U-shaped structure, facing a gate structure in the trenches on those opposite sides, forming a two sided surround transistor. Optionally, the space between the pillars of a pair is also filled with gate electrode material to define a three-sided surround gate transistor. One of the source/drain regions of each pair extending to a digit line and the other extending to a memory storage device, such as a capacitor. The invention also includes methods of forming semiconductor structures.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/490,294 (filed 20 Jul. 2006), which is a divisional of U.S.application Ser. No. 10/933,062, now U.S. Pat. No. 7,442,976, filed onSep. 1, 2004, titled DRAM Cells with Vertical Transistors. The entiretyof these priority applications is hereby incorporated by referenceherein.

This application is related to U.S. application Ser. No. 10/855,429, nowU.S. Pat. No. 7,098,105, filed on May 26, 2004, titled Methods forForming Semiconductor Structures, U.S. application Ser. No. 11/406,455,filed on Apr. 18, 2006, titled Semiconductor Structures And MemoryDevice Constructions, and U.S. application Ser. No. 11/201,824, now U.S.Pat. No. 7,391,070, filed on Aug. 10, 2005, titled SemiconductorStructures And Memory Device Constructions, the entirety of which arehereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor structures, memory deviceconstructions, and methods for forming semiconductor structures.

2. Description of the Related Art

Integrated circuit designers often desire to increase the level ofintegration or density of elements within an integrated circuit byreducing the size of the individual elements and by reducing theseparation distance between neighboring elements. One example of acommon integrated circuit element is a transistor, which can be found inmany devices, such as memory circuits, processors, and the like. Atypical integrated circuit transistor comprises a source, a drain, and agate formed at the surface of the substrate.

A relatively common semiconductor device is a memory device, with adynamic random access memory (DRAM) cell being an exemplary memorydevice. A DRAM cell comprises a transistor and a memory storagestructure, with a typical memory storage structure being a capacitor.Modern applications for semiconductor devices can utilize vast numbersof DRAM unit cells.

It would therefore be desirable to develop new methods for fabricatingsemiconductor devices. It would also be desirable to develop newsemiconductor device constructions that can be utilized in semiconductorapplications, such as DRAM structures.

SUMMARY OF THE INVENTION

In one embodiment, the invention encompasses a method of forming asemiconductor structure. A lattice, having horizontal segments andvertical segments, is etched into a semiconductor substrate, such as asilicon wafer or a portion of bulk silicon. In a further embodiment, anepitaxial layer is grown on the semiconductor substrate prior to formingthe lattice. Etching the lattice into the semiconductor substrate formsrepeating regions of silicon spaced from one another by segments of thelattice. The repeating regions form an array of silicon pillars having afirst pitch along a first axis and a second pitch along a second axis.The second axis is substantially orthogonal to the first axis. Thesecond pitch is approximately twice as big as the first pitch. Pairs ofsilicon pillars form U-shaped transistors.

A first portion of the horizontal lattice segments is etched to a firstdepth, and a second portion of the horizontal lattice segments is etchedto a second depth. The first depth is less than the second depth.Horizontal lattice segments having the first depth alternate withhorizontal lattice segments having the second depth. In an embodiment,the first portion of horizontal lattice segments are filled with a firstmaterial, and the second portion of horizontal lattice segments arefilled with a second material. Each pillar in the U-shaped transistor isseparated from the other pillar in the U-shaped transistor by the firstmaterial and one U-shaped transistor is separated from another U-shapedtransistor by the second material. Preferably, the first material andthe second material are an oxide-containing material. In anotherembodiment, the first material is a nitride-containing material and thesecond material is an oxide-containing material.

The vertical lattice segments are etched to a third depth. Preferably,the third depth is greater than the first depth and less than the seconddepth. In an embodiment, the vertical lattice segments are filled withinsulators and conductors forming the gates of the DRAM transistors.

In one embodiment, the invention encompasses a semiconductor structure.The structure includes semiconductor substrate and a gate line latticeformed into the semiconductor substrate. The lattice defines an array ofnon-gate line regions spaced from one another by segments of thelattice. The array has a first pitch along a first axis and a secondpitch along a second axis substantially orthogonal to the first axis.The second pitch is about twice as big as the first pitch. The non-gateline regions comprise vertically extending source/drain regions.

In another embodiment, the invention encompasses a memory deviceconstruction. The construction includes a semiconductor substrate and agate line etched into the semiconductor substrate. The constructionfurther includes a first vertically extending source/drain region and asecond vertically extending source/drain region, both regions formedfrom the substrate, and at least partially surrounded by the gate line.The source/drain regions are gatedly connected to one another throughthe gate line. A memory storage device is electrically connected to thefirst source/drain region. A digit line is electrically connected to thesecond source/drain region.

In an aspect of the invention, a method for forming a transistor for anintegrated circuit comprises etching a semiconductor substrate to form aU-shaped silicon pillar pair and etched regions surrounding the U-shapedsilicon pillar pair, where the silicon pillar pair comprises a firstpillar and a second pillar. The method further comprises forming a firstsource/drain region in the first pillar, and forming a secondsource/drain region in the second pillar. The method further comprisesforming a gate line in at least a portion of the etched regions, wherethe gate line at least partially surrounds the first and second pillars,and where the first source/drain region, the second source/drain regionand at least a portion of the gate line form a U-shaped transistor.

In another aspect, a method for forming a semiconductor device comprisesetching a first set of trenches to a first depth into a semiconductorsubstrate. The method further comprises etching a second set of trenchesto a second depth into the semiconductor substrate, where the first setof trenches is substantially parallel to the second set of trenches, andwhere the first set of trenches and the second set of trenches arealternately spaced from one another within the semiconductor substrate.The method further comprises etching a third set of trenches to a thirddepth into the semiconductor substrate, where the third set of trenchesis substantially orthogonal to the first set of trenches and to thesecond set of trenches. The first, second and third sets of trenchesdefine an array of vertically extending pillars, wherein the array ofvertically extending pillars comprises vertical source/drain regions. Agate line is formed within at least a portion of the third set oftrenches, where the gate line and the vertical source/drain regions forma plurality of transistors in which pairs of the source/drain regionsare connected to one another through a transistor channel.

In another aspect, a method for forming a memory array comprisesapplying a device mask to a semiconductor substrate to form a firstpattern of alternating first lines and first gaps on the semiconductorsubstrate. The method further comprises processing the semiconductorsubstrate to form a first set of trenches, where the first set oftrenches are formed within the semiconductor substrate within at least aportion of the area defined by the first gaps. The method furthercomprises applying a periphery mask to the semiconductor device afterforming the first set of trenches, where the periphery mask protects aperiphery adjacent an array region. The method further comprisesprocessing the semiconductor substrate to form a second set of trenchessubstantially parallel to the first set of trenches, where the secondset of trenches are formed within the semiconductor substrate within atleast a portion of the array region. The method further comprisesapplying a wordline mask to the semiconductor device to form a secondpattern of alternating second lines and second gaps on the semiconductorsubstrate after forming the second set of trenches, where the secondlines and second gaps intersect with paths of the first lines and firstgaps, and processing the semiconductor substrate to form a third set oftrenches, where the third set of trenches are formed within thesemiconductor substrate within at least a portion of the area defined bythe second gaps, and not formed in the protected periphery.

In another aspect, a method for forming a plurality of U-shapedtransistors in a semiconductor structure comprises separating first andsecond pillars of each U-shaped transistor by a plurality of firsttrenches, and separating each U-shaped transistor from an adjacentU-shaped transistor by a plurality of second trenches that extend deeperinto the semiconductor substrate than the first trenches.

In another aspect, an integrated circuit comprises a semiconductorsubstrate, and first and second U shaped transistors formed within thesemiconductor substrate. The first and second U shaped transistors areseparated by a first trench that extends deeper into the semiconductorsubstrate than the first and second U shaped transistors. Thesemiconductor structure further comprises a second trench that separatesthe first and second U shaped transistors from third and fourth U shapedtransistors, where the second trench extends into the semiconductorsubstrate and is shallower than the first trench.

In another aspect, a memory cell comprises a semiconductor substrate,and a U shaped transistor formed within the semiconductor substrate. TheU-shaped transistor comprises a first pillar and a second pillar, wherethe first and second pillars are separated by a trench that extends intothe semiconductor substrate. The semiconductor structure furthercomprises a memory storage device connected to the first pillar, and adigit line connected to the second pillar.

In another aspect, a semiconductor structure comprises a plurality ofcolumns of protrusions. Each protrusion includes a source, a drain, anda channel. The semiconductor structure further comprises a plurality ofwordline gaps separating the columns from one another. The structurefurther comprises a plurality of gate lines formed within a portion ofthe wordline gaps. Each of the gate lines at least partially surroundsone of the columns.

In another aspect, an electronic device comprises at least one U-shapedsemiconductor structure having a first U-shaped surface and a secondU-shaped surface on opposite sides connected by end-walls. The first andsecond U-shaped surfaces are substantially parallel. The U-shapedsemiconductor structure comprises a first source/drain region and asecond source/drain region. The electronic device further comprises afirst channel formed along the first U-shaped surface, and a secondchannel formed along the second U-shaped surface. The electronic devicefurther comprises a gate line facing both U-shaped surfaces, and a fieldisolation element directly adjacent each end-wall.

In another aspect, a method of forming a memory cell comprises etching asemiconductor substrate to form at least one U-shaped transistor havinga first U-shaped surface and a second U-shaped surface. The first andsecond U-shaped surfaces are substantially parallel. The U-shapedtransistor comprises a first source/drain region, a second source/drainregion, and a gate line, wherein the first source/drain region and thesecond source drain region are formed within the semiconductorsubstrate. The method further comprises forming a first channel withinthe semiconductor substrate along the first U-shaped surface, andforming a second channel within the semiconductor substrate along thesecond U-shaped surface. The method further comprises forming the gateline facing each of the first and second channels.

In another aspect, a method of forming a semiconductor structurecomprises etching a set of wordline trenches within a semiconductorsubstrate, and etching a set of deep trenches within a semiconductorsubstrate. The second set of trenches crosses and creates a grid withthe set of wordline trenches, where the set of wordline trenches and theset of deep trenches define a plurality of protrusions within thesemiconductor substrate. The method further comprises defining a heavilydoped region and a lightly doped region within each protrusion,depositing gate material into the set of wordline trenches, and spaceretching the gate material to define a gate electrode on sidewalls of theprotrusion.

In another aspect, a semiconductor structure comprises a semiconductorsubstrate, and a U-shaped protrusion surrounded by a set of wordlinetrenches and a set of deep trenches etched into the semiconductorsubstrate. The U-shaped protrusion comprises a first pillar and a secondpillar. The first and second pillars are separated by a shallow trenchof a set of shallow trenches that extends into the semiconductorsubstrate and the first and second pillars are connected by a ridge thatextends above the surrounding trenches. The structure further comprisesa first source/drain region formed at a top portion of the first pillar,a second source/drain region formed at a top portion of the secondpillar, and a gate structure formed in the set of wordline trenches. Theridge and the lower portions of the first and second pillars defineU-shaped channels on opposite sides of the U-shaped protrusion. TheU-shaped channels face the gate structure formed in the set of wordlinetrenches.

A lattice and array semiconductor structure constructed above thesubstrate is disclosed in U.S. patent application Ser. No. 10/855,429,by Werner Juengling, Attorney Docket No. MI22-2456, titled SemiconductorStructures, Memory Device Constructions, and Methods for FormingSemiconductor Structures, filed May 26, 2004, the entirety of which ishereby incorporated herein by reference.

For purposes of summarizing the invention, certain aspects, advantagesand novel features of the invention have been described herein. It is tobe understood that not necessarily all such advantages may be achievedin accordance with any particular embodiment of the invention. Thus, theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other advantages as may be taught or suggestedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

A general architecture that implements the various features of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention. Throughout the drawings, reference numbers are re-used toindicate correspondence between referenced elements.

FIG. 1 illustrates a perspective view of an embodiment of asemiconductor device in which an array of transistors can be formed.Views taken along line A-A show a first cross-section of thesemiconductor device and views taken along line B-B show a secondcross-section of the semiconductor device.

FIG. 2 illustrates a cross-sectional view taken along line A-A of anembodiment of the semiconductor device after the formation of additionalsemiconductor processing layers,

FIG. 3 illustrates a top plan view of an embodiment of a photo mask tobe applied to the device illustrated in FIG. 2.

FIG. 4 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 2 after the photo mask of FIG. 3 hasbeen applied and transferred to pattern the hard mask layer.

FIG. 5 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 4 after transferring the pattern intothe oxide layer and removing the hardmask.

FIG. 6 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 5 after deposition of a blanket layerof spacer material.

FIG. 7 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 6 after a spacer etch.

FIG. 8 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 7 after the formation of the first setof trenches.

FIG. 9 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 8 after filling the first set oftrenches.

FIG. 10 illustrates a top plan view of an embodiment of a photo mask tobe applied to the device illustrated in FIG. 9.

FIG. 11 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 9 after removal of the top oxide.

FIG. 12 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 11 after the formation of the secondset of trenches.

FIG. 13 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 12 and also illustrates across-sectional view of the contact trench after filling the second setof trenches and the contact trench.

FIG. 14 illustrates a cross-sectional view taken along line A-A of anembodiment of the device of FIG. 13 after planarizing the surface.

FIG. 15 illustrates a perspective view of an embodiment of the device ofFIG. 14.

FIG. 16 illustrates a top plan view of an embodiment of a photo mask tobe applied to the device illustrated in FIGS. 14 and 15.

FIG. 17 illustrates a cross-sectional view taken along line B-B of anembodiment of the device of FIG. 15 after the photo mask of FIG. 16 hasbeen applied to pattern a hard mask layer.

FIG. 18 illustrates a cross-sectional view taken along line B-B of anembodiment of the device of FIG. 17 after the formation of the third setof trenches orthogonal to the first and second set of trenches.

FIG. 19 illustrates a cross-sectional view taken along line B-B of anembodiment of the device of FIG. 18 after the formation of the gatedielectric and gate electrode layer.

FIG. 20 illustrates a cross-sectional view taken along line B-B of anembodiment of the device of FIG. 19 after a spacer etch, and recessingthe gate electrode layer and the dielectric layer.

FIG. 21 illustrates a cross-sectional view taken along line B-B of anembodiment of the device of FIG. 20 after reoxidizing the device to formthe bird's beaks and forming insulating spacers on top of the recessedgate electrode and gate dielectric layers.

FIG. 22 illustrates a cross-sectional view taken along line B-B of anembodiment of the device of FIG. 21 after depositing a metal layer andperforming a self-aligned silicidation process.

FIG. 23 illustrates a cross-sectional view taken along line B-B of anembodiment of the device of FIG. 22 after filling the third set oftrenches and planarizing the surface.

FIG. 24 illustrates a schematic top plan view of an embodiment of thedevice of FIG. 23.

FIG. 25 illustrates a perspective view of U-shaped protrusions of thetransistors and trenches of FIGS. 23 and 24, shown without fillermaterial for purposes of illustration.

FIG. 26 illustrates a cross-sectional view of an embodiment of aU-shaped transistor, showing n+ source and drain regions, a p-channel,and the relative location of the gate electrode.

FIG. 27 is a schematic diagram depicting communication between amicroprocessor and a memory device.

FIG. 28 is a circuit diagram of a memory array containing multiplewordlines and digit lines.

FIG. 29 illustrates a schematic cross-section of a portion of a memoryarray.

FIG. 30 is a schematic top plan view of a portion of a memory arrayillustrating an embodiment of a wordline for use with the preferredembodiments.

FIG. 31 is a schematic top plan view of a portion of a memory arrayillustrating another embodiment of a wordline for use with the preferredembodiments.

FIG. 32 is a schematic top plan of a portion of a memory arrayillustrating another embodiment of a wordline.

FIG. 33 illustrates a cross-sectional view, taken along line A-A of FIG.32, of a three-sided transistor.

FIG. 34 illustrates a cross-sectional view taken along line B-B of FIG.32.

FIG. 35 is a cross-sectional view taken along line C-C of FIG. 32,showing an inverted U-shaped gate layer for a three-sided transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A device is disclosed for use in a semiconductor structure such as amemory array, a wordline, a transistor, or any other structure.

FIG. 1 is a perspective view of an in-process semiconductor device 100in which a transistor can be formed. In an embodiment, the device 100comprises a memory array. The device 100 includes a semiconductorsubstrate 110, which may comprise any of a wide variety of suitablematerials. The semiconductor substrate 110 may include semiconductorstructures and/or other layers that have been fabricated thereon or anydoped silicon platform that is commonly used in the art. While theillustrated semiconductor substrate 110 comprises an intrinsically dopedmonocrystalline silicon wafer, those of ordinary skill in the art willunderstand that the semiconductor substrate 110 in other arrangementscan comprise other forms of semiconductor layers which include otheractive or operable portions of semiconductor devices.

In an optional embodiment, an epitaxial layer 104 is grown on thesubstrate 110. The epitaxial layer 104 is a semiconductor layer (e.g.,silicon) grown on the substrate 110 by an epitaxial growth process toextend the wafer's crystal structure. In an embodiment, the epitaxiallayer 104 has a thickness preferably within the range of about 2 μm toabout 6 μm, more preferably within the range of about 3 μm to about 5μm. In the case that the epitaxial layer 104 is grown on the substrate110 prior to the etching steps described below, the epitaxial layer 104shall be considered part of the substrate 110. As will be understood inview of the description of FIG. 26 below, the epitaxial layer 104 can beheavily doped with a conductivity type opposite to that of thebackground substrate doping to serve as the active areas of thetransistor(s) being formed.

Views taken of a plane formed by slicing the device 100 along line A-Ashow a first cross-section of the semiconductor device 100 and viewstaken of a plane formed by slicing the device 100 along line B-B show asecond cross-section of the semiconductor device 100 at various stagesof the fabrication process described below.

FIG. 2 illustrates the first cross-section of the device 100. Asillustrated in FIG. 2, the semiconductor device 100 further comprises alayer of material 210 formed over the substrate 110 and the optionalepitaxial layer 104.

Preferably, the material 210 can be etched selectively with respect tothe substrate 110 (silicon) and silicon nitride, and the substrate 110and the silicon nitride can each be selectively etched with respect tothe material 210.

In an embodiment, the material 210 comprises an oxide, such as, forexample, silicon dioxide, having a thickness preferably within the rangeof about 1,000 Å to about 5,000 Å, and more preferably within the rangeof about 2,000 Å to about 3,000 Å. The material 210 can be depositedusing any suitable deposition process, such as, for example, chemicalvapor deposition (CVD) or physical vapor deposition (PVD).

The semiconductor device 100 further comprises a layer of material 212formed over the oxide layer 210 and suitable to be used as a hard mask,in accordance with an embodiment of the invention. In a preferredembodiment, the hard mask 212 comprises amorphous carbon. In otherembodiments, the hard mask 212 can comprise tetraethylorthosilicate(TEOS), polycrystalline silicon, Si₃N₄, SiO₃N₄, SiC, or any othersuitable hard mask material. The material 212 can be deposited using anysuitable deposition process, such as, for example, chemical vapordeposition (CVD) or physical vapor deposition (PVD). In anotherembodiment, the material 212 is photoresist used in a photolithographyprocess.

FIG. 3 illustrates a portion of a photo mask 300 to be applied to thedevice 100 to pattern the hard mask layer 212. The shaded portion of thephoto mask 300 represents the area in which the hard mask 212 willremain after applying photolithography and etching techniques, and theunshaded portion represents the area in which the hard mask 212 will beremoved. The mask 300 forms a pattern of spaced lines 302 separated fromone another by gaps 304. The lines 302 and the gaps 304 extend along ahorizontal direction.

In an embodiment, the lines 302 are approximately 1100 Å toapproximately 1300 Å wide and the gaps 304 are approximately 700 Å toapproximately 900 Å wide.

Preferably, the mask 300 further comprises contact gaps 306, which arewider than gaps 304, and extend in the horizontal direction. In anembodiment, the contact gaps 306 provide an area on the device 100 forplacement of a contact, such as, for example, a wordline contact, aswill be better understood from the discussion of FIG. 30 below.

FIG. 4 illustrates the device 100, from the same view as the firstcross-section, after applying the photo mask 300 (FIG. 3), andpatterning the hard mask 212. As illustrated in FIG. 4, the hard mask212 remains over areas of the substrate 110 where the mask 300 (FIG. 3)forms lines 302. The hard mask 212 is removed, however, from the areaover the substrate 110 where the mask 300 forms gaps 304.

The hard mask 212 can be patterned using well-known photolithography andetching techniques. For example, in some embodiments, photoresist isdeposited as a blanket layer over the device 100 and exposed toradiation through a reticle. Following this exposure, the photoresistfilm is developed to form the photoresist mask 300 (FIG. 3) on thesurface of the hard mask 212, and the hard mask 212 is etched throughthe mask 300 to expose the oxide 210 of the device 110 in the gaps 304.In the illustrated embodiment, features of the hard mask 212 or theprior photo mask 300 are shrunk by isotopic etch, widening the gapsbetween the features.

FIG. 5 illustrates the device 100 of FIG. 4 from the same view as thefirst cross-section, after etching the oxide 210 and removing the hardmask 212.

In some embodiments, the oxide 210 is etched using a process such as,for example, ion milling, reactive ion etching (RIE), or chemicaletching. If an etching process involving a chemical etchant (includingRIE) is selected, any of a variety of well-known etchants can be used,such as for example, CF₄.

As illustrated in FIG. 5, the etching process etches the oxide 210 inthe areas over the substrate 110 where the mask 300 (FIG. 3) or the hardmask 212 (FIG. 4) forms gaps 304, exposing the substrate 110. The oxide210 remains over areas of the substrate 110 where the mask 300 (FIG. 3)or the hard mask 212 (FIG. 4) forms lines 302.

FIG. 6 illustrates the device 100 of FIG. 5, from the same view as thefirst cross-section, after forming a layer spacer of material 602 overthe oxide 210. Preferably, the spacer material 602 fills approximately1/20 to ⅓ of the gaps 304. Preferably, the spacer material 602 can beselectively etched with respect to the substrate 110 (silicon) and theoxide 210, and the substrate 110 (silicon) and the oxide 210 can each beselectively etched with respect to the spacer material 602. In anembodiment, the layer of spacer material 602 comprises anitride-containing material, such as, for example, silicon nitride,having a thickness preferably within the range of about 150 Å to about250 Å, and more preferably within the range of about 180 Å to about 220Å. The material 602 can be deposited using any suitable depositionprocess, such as, for example, chemical vapor deposition (CVD) orphysical vapor deposition (PVD).

FIG. 7 illustrates the device 100 of FIG. 6 from the same view as thefirst cross-section, after forming nitride spacers 702. In anembodiment, an anisotropic etch preferentially removes horizontalsurfaces and patterns the nitride layer 602 into the spacers 702 in awell-known spacer etch process. The spacers 702 form within the gaps 304to narrow the gaps 304. The spacers 702 extend longitudinally in thehorizontal direction along lateral interior peripheries of the gaps 304,and have a width preferably within the range of about 150 Å to about 250Å, and more preferably within the range of about 180 Å to about 220 Å.

FIG. 8 illustrates the device 100 of FIG. 7 from the same view as thefirst cross-section, after etching a plurality of first or “shallow”trenches 800 into the silicon substrate 110. The first trenches 800 areetched into the silicon substrate 110 at the gaps 304 using a processsuch as, for example, ion milling, reactive ion etching (RIE), orchemical etching. If an etching process involving a chemical etchant(including RIE) is selected, any of a variety of well-known etchants canbe used, such as for example, Cl₂.

The first or shallow trenches 800 have a depth preferably within therange of about 2,700 Å to about 3,300 Å, and more preferably within therange of about 2,850 Å to about 3,150 Å. The first trenches 800 have awidth preferably within the range of about 170 Å to about 430 Å, andmore preferably within the range of about 200 Å to about 400 Å. Thetrenches 800 extend longitudinally in the horizontal direction of thedevice 100. See FIG. 3.

FIG. 9 illustrates the device 100 of FIG. 8, from the same view as thefirst cross-section, after depositing a layer of material 900 to fillthe first trenches 800. The material 900 can be deposited using anysuitable deposition process, such as, for example, chemical vapordeposition (CVD) or physical vapor deposition (PVD). Preferably, thematerial 900 can be selectively etched with respect to the substrate 110(silicon) and the nitride 702. In an embodiment, the material 900comprises an oxide, such as, for example, silicon dioxide.

In a second embodiment, the material 900 can preferably be selectivelyetched with respect to the substrate 110 (silicon) and the oxide 210,and the substrate 110 (silicon) and the oxide 210 can each beselectively etched with respect to the material 900. In the secondembodiment, the material 900 comprises a nitride, such as, for example,silicon nitride. See the discussion of FIGS. 32-35 for an understandingof the second embodiment.

FIG. 10 illustrates a photo mask 1000 to be applied to the device 100 ofFIG. 9. As described above, a typical masking process is used. In anembodiment, after depositing a layer of hard mask material to the device100, conventional photolithography, and etching techniques are appliedto etch the hard mask. The shaded portion of the photo mask 1000represents the area in which the hard mask layer remains after applyingconventional photolithography and etching techniques. The remaining hardmask layer protects the periphery of the device 100 from furtherprocessing.

The unshaded portion of the photo mask 1000 represents the area in whichthe conventional photolithography and etching techniques remove the hardmask layer. The removal of the hard mask layer from the surface ofdevice 100 within the area defined by the unshaded portion of the mask1000 permits further processing of the device 100 within the areadefined by the unshaded portion of the mask 1000.

Preferably, the width of the mask 300 (FIG. 3) is narrower than thewidth of the opening of the mask 1000 and the length of the mask 300(FIG. 3) is shorter than the length of the opening of the mask 1000.

FIG. 11 illustrates the device 100 of FIG. 9 from the same view as thefirst cross-section, after removing the oxide 210. The removal of theoxide 210 creates gaps 1100 between the first trenches 800. The oxide210 is etched down to the surface of the substrate 110 using a processsuch as, for example, reactive ion etching (RIE). RIE is a directionalanisotropic etch having both physical and chemical components. Anexample of the physical etching process used in RIE is sputter etching.

As illustrated in FIG. 11, a second spacer 1102 is preferably formedbeside the nitride spacer 702 in the gaps 1100 left by the oxideremoval. In an embodiment, the spacer 1102 comprises anitride-containing material, such as, for example, silicon nitride,having a thickness preferably within the range of about 360 Å to about440 Å, and more preferably within the range of about 380 Å to about 420Å.

In an embodiment, a process, such as an anisotropic etch, forms spacers1102 from a layer of nitride-containing material deposited on thesurface of the device 100. This process is similar to the process usedto form the spacers 702, as described above. The spacer 1102 formsbeside the spacer 702 and within the gap 1100 to narrow the gap 1100.The spacers 1102 preferably fill approximately 1/20 to ⅔ of the gap1100, narrowing the gap 1100 to a width preferably within the range ofabout 360 Å to about 440 Å, and more preferably within the range ofabout 380 Å to about 420 Å. The spacers 1102 extend longitudinally inthe horizontal direction along lateral interior peripheries of the gaps1100.

FIG. 12 illustrates the device 100 of FIG. 11, from the same view as afirst cross-section, after etching a plurality of second or “deep”trenches 1200. The second trenches 1200 are etched into the siliconsubstrate 110 at the gaps 1100 preferably using a directional processsuch as, for example, ion milling, or reactive ion etching (RIE), whichselectively etches the silicon substrate 110 and does not etch the oxideand nitride materials.

The second or deep trenches 1200 have a depth preferably within therange of about 4,500 Å to about 5,500 Å, and more preferably within therange of about 4,750 Å to about 5,250 Å. The second trenches 1200 have awidth preferably within the range of about 170 Å to about 430 Å, andmore preferably within the range of about 200 Å to about 400 Å. Thesecond trenches 1200 extend longitudinally in the horizontal directionof the device 100.

Preferably, as illustrated, the second trenches 1200 are deeper than thefirst trenches 800.

FIG. 13 illustrates the device 100 of FIG. 12 from the same view as thefirst cross-section, after filling the second trenches 1200 with amaterial 1300. Preferably, the material 1300 can be selectively etchedwith respect to the substrate 110 (silicon) and silicon nitride, and thesubstrate 110 and the silicon nitride can each be selectively etchedwith respect to the material 1300. In an embodiment, the material 1300comprises an oxide, such as, for example, silicon dioxide. The material1300 can be deposited using any suitable deposition process, such as,for example, CVD, but is preferably by spin on glass (SOG) deposition.The material 1300 will serve as a field isolation element in the finalstructure as will be seen in the discussion below.

FIG. 13 also illustrates a contact trench 1302 formed by processing thecontact gap 306. The contact trench 1302 is preferably simultaneouslyetched and filled during the process utilized to form the second trench1200, as described above.

The contact trenches 1302 have a depth preferably within the range ofabout 4,500 Å to about 5,500 Å, and more preferably within the range ofabout 4,750 Å to about 5,250 Å. The contact trenches 1302 have a widthpreferably within the range of about 4F to about 6F, or about 2-3lengths of the U-shaped devices. The contact trenches 1302 extendlongitudinally in the horizontal direction of the device 100.

FIG. 14 illustrates the device 100 of FIG. 13 from the same view as thefirst cross-section, after the planarizing the surface of the device100. Any suitable planarization process, such as, for example, chemicalmechanical planarization (CMP) may be used.

As illustrated in FIG. 14, the device 100 comprises pairs of “bulk”silicon pillars 1400. Each second or deep trench 1200, filled with oxide1300 in the illustrated embodiment, separates one pair of “bulk” siliconpillars 1400 from the next pair of “bulk” silicon pillars 1400. The moreshallow first trench 800, filled with oxide or nitride 900 in theillustrated embodiment, separates a first silicon pillar 1402 from asecond silicon pillar 1404 in each pair of silicon pillars 1400.

FIG. 15 illustrates a perspective view of the device of FIG. 14. Thefirst or shallow trenches 800, the second or deep trenches 1200, thecontact trenches 1302, and the silicon pillars 1400 extendlongitudinally in the horizontal direction of the device 100.

Referring to FIG. 3, the photo mask 300 defines the lines 302 and gaps304 etched into the device 100. By performing the processing steps asdescribed above, the line and gap features 302, 304 of the photo mask300 form the trenches 800, 1200 and the pillars 1402, 1404. Due to theformation of spacers protecting the silicon substrate 110 during theetching processes, the device 100 comprises approximately two pillars1402, 1404 for every one of the line and gap photo features 302, 304 ofthe mask 300. The distance between identical, adjacent features of thephoto mask 300 is approximately twice as big as the distance between thesilicon pillars 1402, 1404, and the more densely packed pillars are saidto be “double pitched” or “pitch multiplied” relative to thelithography-defined critical dimension.

FIG. 16 illustrates a portion of a third photo mask 1600 to be appliedto the device 100 of FIG. 15. The mask 1600 forms a pattern of isolatedlines 1602 within an opening. The lines 1602 are separated from oneanother by gaps 1604. The lines 1602 and the gaps 1604 extend along avertical direction. The third mask 1600 also forms an area between thepattern of spaced lines 1602 and gaps 1604 and the array-bounding secondmask 1000.

Referring to FIG. 7, the spacers 702 form along the lateral sides andends of the rows of oxide 210 remaining in the lines 302, forming a looparound the end of each row of oxide 210. In addition, referring to FIG.11, the spacers 1102 form along the lateral sides and ends of thespacers 702, forming a loop around the shallow trench 800. During anetching process described below, the area of the third mask surroundingthe pattern of spaced lines 1602 and gaps 1604 causes the loop ofspacers 702 and 1102 around the shallow trench 800 to be etched away.Thus, the spacers 702, 1102 extend longitudinally in the horizontaldirection along lateral interior peripheries of the gaps 1100, forminglines, and not forming loops at the periphery of the device 100.

FIG. 17 illustrates the device of FIG. 16 after the pattern of the photomask 1600 has been transferred to an underlying layer of hard maskmaterial 1700. FIG. 17 illustrates the view of the device 100 into theplane formed by slicing device 100 along the line B-B, or from the viewof a second cross-section, orthogonal to the first cross-section.

In an embodiment, using a carbon shrink process to further reduce theline width to less than F, where F is the minimum printable size of afeature of a photo mask, the lines 1602 are 0.5F wide and the gaps 1604are 1.5F wide. The carbon shrink process does not change the pitch ofthe mask 1600. The shaded portions, the lines 1602, of the photo mask1600 represent the area in which a hard mask layer remains afterapplying photolithography and etching techniques, and the unshadedportions, the gaps 1604 and the border 1606 (FIG. 16), represent thearea in which the hard mask layer is removed.

As described above, a typical masking process is used. After depositinga layer of hard mask material 1700, the hard mask 1700 can be patternedusing well-known photolithography and etching techniques. For example,in some embodiments, photoresist is deposited as a blanket layer overthe device 100 and exposed to radiation through the photo mask 1600.Following this exposure, the photoresist film is developed to form aphotoresist mask on the surface of the hard mask 1700, and the hard mask1700 is etched to expose the substrate 110 in the gap regions 1604 andthe border region 1606 (FIG. 16) of the device 100.

As illustrated in FIG. 17, the hard mask 1700 remains over the area ofthe substrate 110 where the third mask 1600 forms lines 1602.Preferably, the lines 1602 are reduced to 0.5F wide using a carbonshrink process, (e.g., by isotropic etching), and the gaps 1604 become1.5F wide, where F is the minimum printable size of a feature of a photomask.

FIG. 18 illustrates the device 100 of FIG. 17 from the same view as thesecond cross-section, after forming a plurality of third or wordlinetrenches 1800 and after removing the hard mask 1700.

The third trenches 1800 are etched into the substrate 110 in the area1604 of the device 100. The silicon substrate 110 and oxide 900, 1300can be etched using any dry etch which etches oxide and bulk silicon atthe same rate. In other embodiments, a first etch etches the siliconsubstrate 110 and a second etch etches the oxide 900, 1300. Alternately,the first etch etches the oxide 900, 1300 and the second etch etches thesilicon substrate 110.

The third or wordline trenches 1800 have a depth preferably within therange of about 3,600 Å to about 4,400 Å, and more preferably within therange of about 3,800 Å to about 4,200 Å. The third trenches 1800 have awidth of approximately 1.5F, or preferably within the range of about1450 Å to about 1780 Å, and more preferably within the range of about1540 Å to about 1700 Å. The third trenches 1302 extend laterally in thehorizontal plane, substantially perpendicular or orthogonal to the firsttrenches 800 and to the second trenches 1200, of the device 100.

Preferably, the third trenches 1800 are deeper than the first trenches800 to allow for the formation of a transistor gate electrode along asidewall of the third trenches 1800. Further, the third trenches 1800are preferably not as deep as the second trenches 1200 to allow thesecond trenches 1200 to provide isolation between closely spacedtransistors when the wordline is enabled.

The device 100 further comprises silicon pillars 1802 formed between thethird trenches 1800.

FIG. 19 illustrates the device 100 of FIG. 18, from the same view as thesecond cross-section, after forming a layer of dielectric material 1902and depositing a layer of material 1904 on the device 100. In anembodiment, the dielectric is a gate oxide comprising silicon dioxide.The dielectric 1902 has a thickness preferably within the range of about50 Å to about 70 Å, and more preferably within the range of about 54 Åto about 66 Å. The dielectric 1902, in an embodiment, can be applied bywet or dry oxidation of the semiconductor substrate 110 followed byetching through a mask, or by dielectric deposition techniques.

In an embodiment, the material 1904 comprises a gate electrode layer,such as, for example, polysilicon, and has a thickness of approximately½F. Preferably, the polysilicon has a thickness of approximately 540 Å,and more preferably within the range of about 490 Å to about 510 Å. Thepolysilicon 1904 can be deposited using any suitable deposition process,such as, for example, chemical vapor deposition (CVD) or physical vapordeposition (PVD).

The polysilicon 1904 is also deposited in the trench formed by etchingthe border area 1606 (FIG. 16).

FIG. 20 illustrates the device 100 of FIG. 19, from the same view as thesecond cross-section, after a spacer etch and etching and recessing thepolysilicon 1904 and the dielectric 1902 to form spacers 2000. Thespacer etch also separates the spacers 2000 at the bottom of the thirdtrench 1800.

Recessing the polysilicon 1904 and the dielectric 1902 to form spacers2000 exposes the upper side portion 2002 of the silicon pillars 1802.The recess is approximately 900 Å to approximately 1100 Å, orapproximately ⅓ of the depth of the trench 1800.

FIG. 21 illustrates the device 100 of FIG. 20 from the same view as thesecond cross-section, after reoxidizing the device 100 and after forminggate isolation spacers 2102.

In some embodiments, the processing steps may cause damage to the gateoxide 1902. The reoxidization process may repair at least a portion ofthe damage to the gate oxide 1902 at the exposed corners: at the top ofthe pillars and at the bottom of the third trench 1800. The regrown gateoxide material 2100 isolates active regions of the transistors from thespacer 2000 at high field corners of the gate electrodes, and forms acharacteristic bird's beak shape after completion of the reoxidizationprocess. The spacer 2000 is the gate electrode or gate layer 2000. In anembodiment, the reoxidation is applied by wet or dry oxidation of thesubstrate 110, or by other common oxidation techniques. In anembodiment, the regrown gate oxide material 2100, which formed on thegate layer 1904, is etched back from the gate layer 1904.

As also illustrated in FIG. 21, the spacers 2102 are formed on theexposed upper side portion 2002 of the silicon pillars 1802. The spacers2102 comprise a nitride-containing material, such as, for example,silicon nitride, and are formed in a process that is similar to theprocess used to form spacers 702, which is described above. The spacers2102 are smaller than the spacers 2000, and reinforce shielding athigh-field corners of the gate to reduce or prevent current leakage andto prevent shorting of the gate to the source/drain from a subsequentsalicide process. The process that forms spacers 2102 also fills the gapbetween the polysilicon spacers 2000 at the bottom of the trench 1800with the nitride-containing material.

FIG. 22 illustrates the device 100 of FIG. 21, from the same view as thesecond cross-section, after forming a conductive layer 2200.

In an embodiment, the polysilicon spacers 2000 are salicided(self-aligned silicidation) to form a layer of conductive material 2200.A metal layer is blanket deposited and an anneal step causessilicidation where ever the metal contacts silicon, such as on the topof the pillars and on the exposed surface of the polysilicon spacers2000. In an embodiment, the silicide material 2200 comprises a siliconand a metal, such as, for example, tungsten, titanium, ruthenium,tantalum, cobalt, and nickel, and is between approximately 100 Å and 300Å thick, and more preferably between approximately 190 Å and 210 Åthick. A selective metal etch removes excess metal and metal that doesnot contact silicon.

The metal silicide forms a self-aligned strapping layer 2200 to increaselateral conductivity along the wordline. The metal silicide also formson the tops of the pillars 1802 to provide source and drain contacts, aswill be better understood from the discussion of FIG. 29 below. Anoptional physical etch ensures the separation of the spacers 2000 at thebottom of the trench 1800.

Those of ordinary skill in the art will recognize that the conductivelayer 2200 may also be made of other metals, such as, for example, gold,copper aluminum, and the like, and need not react with the silicon.Mixtures of metals are also suitable for forming the conductive layer2200. If the metal strapping layer 2200 is not formed by a salicideprocess, then the preferred process is selective deposition on silicon.Other methods of depositing the conductive layer 2200 include, but arenot limited to, rapid thermal chemical vapor deposition (RTCVD), lowpressure chemical vapor deposition (LPCVD), and physical vapordeposition (PVD).

FIG. 23 illustrates the device 100 of FIG. 22 from the same view as thesecond cross-section, after filling the remainder of the third trenches1800 with an insulating material 2300. In an embodiment, the insulatingmaterial 2300 comprises an oxide such as, for example, silicon dioxide.The insulating material 2300 can be deposited using any suitabledeposition process, such as, for example, SOD, CVD, or PVD.

FIG. 23 also illustrates the device 100 after planarization. Anysuitable planarization process, such as, for example, chemicalmechanical polishing (CMP) may be used. The CMP slurry is preferablyselective versus the silicide to protect the contacts on the pillartops.

From the view of the second cross-section, the device 100 comprises arow of silicon pillars 1802 separated from one another by the pluralityof oxide filled third trenches 1800. The silicon pillars 1802 arepreferably approximately 410 Å to 510 Å wide, and more preferably 440 Åto 480 Å wide. The third trenches 1800 further comprise the gatedielectric 1902, the gate layer 2000, and the conductive strapping layer2200.

FIG. 24 illustrates a top view of the device 100. The device 100comprises an array of silicon pillars 1802, the first or shallowtrenches 800, the oxide-filled second or deep trenches 1200, and theoxide-filled third or wordline trenches 1800. The first or shallowtrenches are filled with oxide in the illustrated embodiment, and filledwith nitride in another embodiment (see FIGS. 32-34 and related text).The device 100 further comprises the dielectric layer 1902 (not shown),the wordline spacer 2000, and the metal strapping layer 2200. Thedielectric layer 1902, which forms only on the sides of the siliconpillars 1802, and is a thin layer separating the wordline spacer 2000from the silicon pillars 1802, is not shown for clarity. The metalstrapping layer 2200 is not shown for clarity.

The array of silicon pillars 1802 has a first pitch 2402 and a secondpitch 2404. The pitch is the distance between repeating elements in thearray. The first pitch 2402 is the width of the silicon pillar 1802 asmeasured in the y-direction plus the distance between silicon pillars1802 as measured in the y-direction. The second pitch 2404 is the lengthof the silicon pillar 1802 as measured in the x-direction plus thedistance between silicon pillars 1802 as measured in the x-direction. Inan embodiment, the second pitch 2404 is approximately twice as big asthe first pitch 2402.

Pairs of pillars 1802 further form protrusions 2406 of verticaltransistors. Each vertical transistor protrusion 2406 comprises twopillars 1802, which are separated by the oxide or nitride-filled firstor shallow trench 800 and connected by a channel base segment 2407 thatextends beneath the shallow trench 800. The vertical transistors 2406are separated from one another in the y-direction by the oxide-filledsecond or deep trenches 1200.

The wordline spacers or wordlines 2000 are separated from one another bythe oxide-filled third or wordline trenches 1800.

FIG. 25 illustrates a perspective view of the silicon pillars 1802 ofthe device 100. The dielectric layer 1902, the wordline 2000, and themetal strapping layer 2200, which are formed in the wordline trench1800, have been left off for clarity. Also, the trenches 800, 1200, 1800are shown unfilled for clarity.

FIG. 25 illustrates a plurality of U-shaped protrusions 2406 formed bythe crossing trenches described above. Each U-shaped protrusion includesa pair of pillars 1802 connected by a channel base segment 2407. EachU-shaped protrusion 2406 includes the source, drain and channel regionsof the vertical transistor. In particular, each pillar 1802 of the pairof pillars 1802 forms a source or a drain region of the transistor. Thefirst trench 800 separates one pillar 1802 of the protrusion 2406 fromthe other pillar 1802 of the protrusion 2406. The second trench 1200separates one transistor protrusion 2406 from another transistorprotrusion 2406 in the y-direction.

Each U-shaped pillar construction has two U-shaped side surfaces facinga wordline trench 1800, forming a two-sided surround gate transistor.Each U-shaped pillar pair comprises two back-to-back U-shaped transistorflow paths having a common source, drain, and gate. Because theback-to-back transistor flow paths in each U-shaped pillar pair sharethe source, drain, and gate, the back-to-back transistor flow paths ineach U-shaped pillar pair do not operate independently of each other.The back-to-back transistor flow paths in each U-shaped pillar pair formredundant flow paths of one transistor protrusion 2406.

When the transistors are active, the current i stays in left side andright side surfaces of the U-shaped transistor protrusion 2406. The leftside and right side surfaces of the U-shaped transistor protrusion 2406are defined by the third or wordline trenches 1800. The current for eachpath stays in one plane. The current does not turn the corners of theU-shaped transistor protrusion 2406. The transistors, in an embodiment,can become fully depleted.

The wordlines 2000 surround a column of U-shaped transistors. The thirdor wordline trench 1800 separates one wordline 2000 from anotherwordline 2000 in the x-direction.

In an embodiment, the second trench 1200 is deeper than the third trench1800, and the third trench 1800 is deeper than the first trench 800.

In an embodiment, the first trench 800 is filled with theoxide-containing material 900, the second trench 1200 is filled with theoxide-containing material 1300, and the third trench 1800 is filled withthe oxide-containing material 2300. Optionally, in another embodiment,the first trench 800 is filled with nitride-containing material, thesecond trench 1200 is filled with oxide-containing material, and thethird trench 1800 is filled with oxide-containing material. Additionalprocessing steps could remove the nitride containing material from thefirst trench 800 and fill the first trench 800 with a conductivematerial, as will be further discussed with respect to the embodiment ofFIGS. 32-35 below.

FIG. 26 illustrates one embodiment of the transistor from the same viewas the first cross-section, in which the gate line spacer 2000 (notshown) gatedly connects the source/drain regions of the transistorprotrusion 2406 to each other. While the gate line spacer 2000 is notshown in FIG. 26 because it is parallel to the plane of view, the heightof the gate line spacer 2000 is indicated by dashed lines 2414, 2416.Dashed line 2416 also indicates the bottom of the third or wordlinetrench 1800.

The transistor protrusion 2406 comprises a first silicon pillar 2600 anda second silicon pillar 2602 connected by the channel base segment 2407.Each of pillars 2600, 2602 has an n+ doped source/drain region in anuppermost portion of the pillar, with the heavily-doped region of pillar2600 being labeled 2604 and the heavily-doped region of pillar 2602being labeled 2606.

The transistor protrusion 2406 further comprises a doped region 2608that extends from the n+ doped region 2606, through the channel basesegment 2407, to the doped region 2604, with such doped region 2608indicated to be p-. The doped region 2608 forms a U-shaped channel ofthe transistor.

The n+ doped source/drain region 2604 of the first pillar 2600 connectswith the n+ doped source/drain region 2606 of the second pillar 2602through the U-shaped channel 2608. The channel length of the transistoris the length extending from source/drain region 2604 to source/drainregion 2606 through the U-shaped channel 2608.

The channel characteristics of the device can be influenced by tailoringthe dopant concentrations and types along the channel length.Additionally, characteristics of the device can be influenced by thetype of materials utilized for pillars 2600 and 2602. Further, thedevice characteristics are influenced by the type of material utilizedfor the gate line spacer 2000 and the thickness of the gate line spacer2000.

Preferably, the semiconductor substrate 110 is doped to create channeland source/drain regions prior to the etch steps described above. In anembodiment, the epitaxial layer 104 is doped to create source/drainregions prior to processing the semiconductor device 100. In anotherembodiment, the semiconductor substrate 110 is doped to createsource/drain regions in additional processing steps during the etchsteps described above. In a further embodiment, the semiconductorsubstrate 110 is doped to create source/drain regions in additionalprocessing steps after the etch steps described above. The semiconductordevice 100 can be doped using any suitable doping process, such as, forexample, ion implantation or diffusion.

FIG. 26 illustrates an exemplary embodiment of the invention, and it isto be understood that the invention also encompasses variousmodifications. For instance, the dopant types shown in FIG. 26 can bereversed relative to the shown embodiment. Thus, all of the n-typeregions can be converted to opposite conductivity (i.e. p-type) regions,and likewise the p-type regions can be converted toopposite-conductivity (i.e. n-type) regions.

FIG. 27 illustrates a memory array 2710 that interfaces with otherelectronic circuitry 2712 via conventional address signals 2714 and datasignals 2716. The address signals 2714 select one or more memory cellsin the memory array 2710. The data signals 2716, on the other hand,carry data that is stored in or retrieved from the memory array 2710.

In one embodiment, the memory array 2710 is a dynamic random accessmemory (DRAM). In other embodiments the memory array 2710 may comprise awide variety of memory devices such as static memory, dynamic memory,extended data out memory, extended data out dynamic random access memory(EDO DRAM), synchronous dynamic random access memory (SDRAM), doubledata rate synchronous dynamic random access memory (DDR SDRAM),synchronous link dynamic random access memory (SLDRAM), video randomaccess memory (VRAM), rambus dynamic random access memory (RDRAM),static random access memory (SRAM), flash memories, or any other memorytype known in the art.

The memory array 2710 interfaces with different types of electroniccircuitry 2712. By way of example, the electronic circuitry 2712 caninclude any device, which accesses or relies on memory including, butnot limited to, computers, and the like.

The computers comprise, by way of example, processors, program logic, orother substrate configurations representing data and instructions, whichoperate as described herein. In other embodiments, the processors cancomprise controller circuitry, processor circuitry, processors, generalpurpose single-chip or multi-chip microprocessors, digital signalprocessors, embedded microprocessors, microcontrollers and the like.

In some embodiments, the memory array 2710 and the electronic circuitry2712 are implemented separately. In other embodiments, the memory array2710 and the electronic circuitry 2712 are integrated together.Furthermore, one of ordinary skill in the art will recognize that thememory array 2710 can be implemented in a wide variety of devices,products, and systems.

FIG. 28 illustrates the memory array 2710 that comprises a plurality ofmemory cells 2820. These memory cells 2820 are organized into columnsC₁-C_(N) and rows R₁-R_(N). A column decoder 2824 and a row decoder 2826process the address signals 2714 to identify the column C_(N) and rowR_(N) of the targeted memory cell 2820. The columns (in the illustratedconfiguration) are commonly known as wordlines and the rows aretypically known as digit lines.

FIG. 29 illustrates a portion of the memory array 2710 formed by thedevice 100. In an embodiment, one of the pillars 1802 of each verticaltransistor connects to a digit line or bitline 2914 (B) and the otherpillar 1802 of the transistor connects to a memory storage device 2910(C), such as, for example, a capacitor, to form a portion of a memorydevice, such as, for example, a DRAM. In an embodiment, the memorystorage device 2910 electrically connects to one of the pillars 1802 ofthe transistor through a plug or contact 2912. The wordline 2000 isindicated by the dashed lines 2414, 2416.

In a typical embodiment, the memory cell 2820, comprising the U-shapedtransistor protrusion 2406, the contact 2912, and the memory storagedevice 2910, and the bitline 2914, occupy a 4F² space in the memoryarray 2710, where F is the minimum printable feature defined by thephotoresist masks 300, 1600. In the embodiment illustrated by FIGS.1-29, the spacers 702, 1102, reduce the F sized features of thephotoresist mask.

FIG. 30 illustrates a portion of a memory array 2710 comprising aplurality of wordlines 2000. The wordline 2000 at least partiallysurrounds the column of U-shaped transistor protrusions 2406. Thecontact trench 1306 along columns of the U-shaped transistor protrusions2406 in the device 100 provides room for a wordline contact from above.

FIG. 31 illustrates another embodiment of the portion of the memoryarray 2710 employing the wordlines 2000. Contacts for the wordlines 2000are placed at the alternating ends of the columns of transistors. Inthis embodiment, the wordlines 2000 are patterned for higher integrationwithin the memory array 2710.

FIGS. 32-35 illustrate another embodiment of a portion of a memory array2710 comprising wordlines 3200. The memory array 2710 further comprisesa plurality of three-sided transistors 3202. Each transistor 3202comprises two silicon pillars 1802 formed as described above withrespect to FIGS. 1-14. The first or shallow trench 800, however, isfilled with a nitride-containing material, such as silicon nitride. Thewordline trench 1800 is formed as described with respect to FIGS. 16-18.

Before forming the gate dielectric 1902 and depositing the gate layer1904 in the wordline trench 1800, as illustrated in FIG. 19, a selectivenitride etch removes the nitride (see FIG. 14) from the shallow trench800.

After the selective nitride etch removes the nitride from the shallowtrench 800, the gate dielectric 1902 is formed, and the gate layer 1904is deposited in the wordline trench 1800, as illustrated in FIG. 19. Thegate dielectric 1902 also forms in the shallow trench 800. Further, thegate layer 1904 is also deposited in the shallow trench 800. Because theshallow trench 800 is narrower than the wordline trench 1800, thedeposition of the gate layer 1904 fills the shallow trench 800.

The spacer etch of the gate layer 1904, illustrated in FIG. 20, recessesthe gate layer 1904 deposited in the shallow trench 800, but does notremove the gate layer 1904 in the shallow trench 800.

The process continues as described in FIGS. 21-23. The device 100 isreoxidized and spacers 2102 are formed (FIG. 21), the conductive layer2200 is formed (FIG. 22), and the device 100 is planarized (FIG. 23).

Referring to FIG. 32, the wordline 3200 formed by the above processdefines a ladder-shaped polysilicon gate layer 3200. The transistors3202 are surrounded on three sides by the ladder-shaped gate layer 3200,forming the three-sided surround gate transistors 3202.

FIG. 33 illustrates a cross-section of the U-shaped transistor 3202 asviewed from the plane formed by line A-A of FIG. 32. The device 100comprises the pair of silicon pillars 1802, the oxide-filled deep trench1200, the shallow trench 800, and the substrate 110. The shallow trench800 comprises the dielectric layer 1902, and is filled with the gatelayer 3200. The sections of the gate layer 3200 that are parallel to theplane of view are indicated by dashed lines. Pairs of pillars 1802 formthe transistors 3202. Each pillar 1802 in the pair of pillars 1802 isseparated from the other pillar 1802 in the pair of pillars 1802 by thepolysilicon-filled shallow trench 800. Each transistor 3202 is separatedfrom another transistor 3202 by the oxide-filled deep trench 1200.

In the illustrated embodiment, each of pillars 1802 has a p+ dopedsource/drain region in an uppermost portion of the pillar. Thetransistor 3202 further comprises an n− doped region that extends fromthe p+ doped region of one pillar 1802 to the p+ doped region of theother pillar 1802. The wordline 3200 is indicated by dashed lines.

FIG. 34 illustrates a cross-section of the memory array 2710 as viewedfrom the plane formed by the line B-B of FIG. 32. The memory array 2710comprises silicon pillars 1802. The silicon pillars 1802 are separatedfrom one another by the oxide-filled third trench 1800. The siliconpillars 1802 are preferably approximately 410 Å to 510 Å wide, and morepreferably 440 Å to 480 Å wide. The memory array 2710 further comprisesthe gate dielectric 1902, the wordline 3200, and the conductivestrapping layer 2200.

FIG. 35 illustrates a cross-section of the memory array 2710 as viewedfrom the plane formed by line C-C of FIG. 32, shown without theconductive strapping layer for convenience. This view illustrates the(partially) polysilicon-filled shallow trench 800, which forms a “rung”of the ladder-shaped gate layer 3200. The bottom 3500 of the shallowtrench 800 defines the lower edge of the “rung” of the ladder-shapedgate layer 3200. The memory array 2710 comprises the silicon pillars1802. The silicon pillars 1802 are separated from one another by theoxide-filled third trench 1800. The oxide-filled third trench 1800comprises the “sides” of the ladder-shaped gate layer 3200. The memoryarray 2710 further comprises the gate dielectric 1902, and theconductive strapping layer 2200.

Methodology of the invention can be used in numerous applications. Forexample, the invention can be utilized for forming one transistor,one-capacitor 4F2 DRAM cells. In particular embodiments, the inventioncan be considered to comprise vertical DRAM cell technology. Onetransistor pillar connects the cell storage device to a substrate, andanother transistor pillar connects the digit line to the substrate. Theself-aligned lateral transistor channel region connects verticalsource/drain region pillars to one another. The cell can have low digitcapacitance and low wordline resistance, Because the U-shaped transistorprotrusions 2406 comprises two U-shaped surfaces that share a commonsource, drain, and gate, the cell can have redundancy against verticalaxis problems.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

1. A transistor comprising: a semiconductor substrate; a U-shapedstructure comprising a first pillar, a second pillar and a channel basesegment connecting bottom portions of the first and second pillars, theU-shaped structure extending from the semiconductor substrate andcomprising a first U-shaped sidewall and a second U-shaped sidewall onopposite sides connected by facing inner walls of the first and secondpillars, an upper surface of the channel base segment and end walls ofthe first and second pillars; a drain region formed at a top of thefirst pillar; a source region formed at a top of the second pillar; afirst U-shaped channel formed along the first U-shaped sidewall, whereinthe first U-shaped channel comprises a horizontal portion along thechannel base segment and vertical portions along the pillars; and afirst gate line facing the first U-shaped sidewall.
 2. The transistor ofclaim 1, further comprising a second U-shaped channel formed along thesecond U-shaped sidewall, wherein the second U-shaped channel comprisesa horizontal portion along the channel base segment and verticalportions along the pillars.
 3. The transistor of claim 2, furthercomprising a second gate line facing the second U-shaped sidewall. 4.The transistor of claim 3, wherein the first and second gate lines areelectrically connected.
 5. The transistor of claim 4, wherein the firstand second gate lines are electrically connected by a gateline rungformed along the inner walls and the upper surface of the channel basesegment.
 6. The transistor of claim 1, wherein the first gate linecomprises portions below the level of the upper surface of the channelbase segment.
 7. The transistor of claim 1, further comprising a fieldisolation element directly adjacent each of the end walls.
 8. Thetransistor of claim 7, wherein the field isolation element extendsdownwardly below the level of the channel base segment.
 9. Thetransistor of claim 1, wherein a height of one of the end walls extendsfrom a floor to a top upper surface of the pillar, wherein the floor issubstantially below a level of the channel base segment.
 10. Atransistor array comprising: a column of U-shaped structures eachcomprising a first pillar, a second pillar and a channel base segmentconnecting bottom portions of the first and second pillars, eachU-shaped structure extending from the semiconductor substrate andcomprising a first U-shaped sidewall and a second U-shaped sidewall onopposite sides connected by facing inner walls of the first and secondpillars, an upper surface of the channel base segment and end walls ofthe first and second pillars; a drain region formed at a top of thefirst pillar of each U-shaped structure; a source region formed at a topof the second pillar of each U-shaped structure; a first U-shapedchannel formed along the first U-shaped sidewall in each U-shapedstructure, wherein each U-shaped channel comprises a horizontal portionalong the channel base segment and vertical portions along the first andsecond pillars; and a first wordline formed along and facing the firstU-shaped sidewalls of the column.
 11. The transistor array of claim 10,wherein the first and second pillars of all of the U-shaped structuresin the column are aligned.
 12. The transistor array of claim 10, furthercomprising a second U-shaped channel formed along the second U-shapedsidewall in each U-shaped structure, wherein each second U-shapedchannel comprises a horizontal portion along the channel base segmentand vertical portions along the first and second pillars.
 13. Thetransistor array of claim 12, further comprising a second wordlineformed along and facing the second U-shaped sidewalls of the column. 14.The transistor array of claim 13, wherein the first and second wordlinesare electrically connected.
 15. The transistor array of claim 14,wherein the first and second wordlines are electrically connected byrungs formed along the inner walls and the upper surfaces of the channelbase segments of the U-shaped structures in the column.
 16. Thetransistor array of claim 14, wherein the first and second wordlines areelectrically connected around a first end wall of a first U-shapedstructure in the column.
 17. The transistor array of claim 14, whereinthe first and second wordlines are electrically connected around a firstend wall of a first U-shaped structure in the column and around anopposite end wall of a last U-shaped structure in the column.
 18. Thetransistor array of claim 10, wherein the first wordline comprisesportions below the level of the upper surface of the channel basesegment.
 19. The transistor array of claim 10, wherein a first U-shapedstructure in the column is separated from an adjacent U-shaped structurein the column by a field isolation element between one end wall of thefirst U-shaped structure and one end wall of the adjacent U-shapedstructure.
 20. The transistor array of claim 19, wherein the fieldisolation element extends downwardly below the level of the channel basesegment.